1. Field of the Invention
The present invention generally relates to a novel lighting circuit for a vehicular discharge lamp. More particularly, this invention pertains to a novel lighting circuit for a vehicular discharge lamp, adapted to boost the voltage from a DC power supply and then convert the voltage into an AC voltage to be applied to a discharge lamp, which lighting circuit reduces power loss originating from heat generation or the like due to reduction in the DC voltage to be supplied to the lighting circuit, thereby preventing the circuit elements from being deteriorated or damaged.
2. Description of the Related Art
Metal halide lamps have recently been receiving greater attention as a light source for vehicular headlamps. To always ensure stable supply of constant power to such a lamp with respect to a variation in a battery voltage is required as one of the important functions of a lighting circuit for the lamp.
A conventional lighting circuit is therefore designed to be able to cope with some fluctuation in battery voltage within the allowable range for the circuit.
Even if the battery voltage drops abnormally, however, the conventional lighting circuit tries to supply the constant power to the lamp. This will troublesomely increase the consumption of the battery current and thus increase the power loss caused by generation of heat or the like.
In particular, if such a reduction in battery voltage continued under a high-temperature environment, it could heat up the circuit elements, thus deteriorating these elements or even destroying them at worst.